Disassembling the Losmandy G11


These webpages were born when I still owned my G11, until the year 2002 or so. More recent models have seen significant improvements, thus a lot of the modifications and tuning described here are now superseeded or superfluous, or maybe even plainly wrong. They only apply to models produced before the year 2000 or so. I moved on to a larger mount a long time ago since my own needs changed, and therefore I cannot reflect the G11's current state in these web pages any more. I will keep these pages alive as they are now, for reference, and because I expect these old sturdy mounts to be around for a significant number of years yet to come. Should any pictures or text presented here about the G11 be of use for your own webpage, then please feel free to use it.

Thank you,

Mischa Schirmer, June 11, 2009

One of the biggest advantages of the G11 is its modularity. It can be very easily taken apart and safely reassembled again. No balls from a ball bearing will accidentally fall out. An elder G11 mount will appreciate a new, fresh load of fine grease, or a readjustment of some parts. See my G11 tuning page for the details. Here I just report how to do the disassembly. Reassembling is in reversed order.
Some images were not taken in chronological order. But I guess you will get the point. If you take apart the mount the very first time, prepare yourself for the unexpected. Some screws could come loose only by brute force. Apply some of your common sense upon reasssembling the mount, there is usually no reason for overtightening (one exception can be the polar block).

Remove the polar finder, the drives and the worms

This is the first you should do when disassembling the G11. After unmounting the polar finder scope, loosen the two tiny allen head screws that hold the boxy worm cover in place, and put it aside. You can now see the worm (Fig. 2). Then remove the flexible plastic cover from the drive, and unscrew the small allen head screws that attach it to the mount. The drive is connected to the worm with a small plastic coupling (Fig. 2). You can simply slide the unit off with a move to the side. Just for fun, try to turn the worm by hand. You should be able to manually turn it, there should be no uneven spots. The worm itself is attached to the base plate from beneath with two allen head screws. Loosen them, and you can remove the worm, too. Do this for both drives.

Fig. 1: You start from here

Fig. 2: Drive without the plastic cap. One can see the white coupling between the drive and the worm.

Fig. 3: G11 without the drive. The big round protective cover for the gear has already been removed, too (three small allen head screws held it from beneath). The worm is still in its place in this picture.

The polar block, the RA block and the DEC block

These are the three main modules of the G11. Lets take off the DEC block first. Remove the four screws that are located around the polar finder cap on the front side of the mount. You can't miss them in Fig 1. Once all four screws are loosened, the DEC block will slide off. Be careful, it is heavy! Its lower side is entirely flat, thus it was only held in place by the four screws on top of the RA block. The flat upper side of the RA block can be seen in Figs. 2 & 3.

In the next step, lets remove the RA block from the polar block. This is a bit cumbersome. First, remove the two big screws that lock the polar altitude of the RA block. You will find a golden colored bolt inside. Stick a stable screw driver or something similar in its hole. Hit it with a hammer until the bolt comes out on the other side. Next, you pull out the RA block of the polar block, but it is not that easy:
Look at the polar block in Fig. 6 (left), you see a second golden bolt there. This bolt sits in the fork-like lower end of the RA block (Fig. 6, middle). You might want to turn the big knob that adjusts the polar altitude a bit forth and back to loosen everything and bring the RA block into a better position. Then simply start pulling and pushing the RA block upwards. It requires quite some effort, but after a while you will see that it comes off. Once you understood the mechanical principle you will realise that there is nothing that can be broken or damaged. All pieces are rock solid.

Fig. 4: The polar block and the RA block. The latter one is attached to the polar block by the two big central screws on the east and west side of the mount. More recent G11 models have a second, off-center locking mechanism which needs to be removed, too.

Fig. 5: The bolt that keeps the RA block in place. It's hard to get out. You want to put some grease on it when assembling the mount again.

Fig. 6: Once done, your mount should look like this: polar block, RA block and DEC block (from left to right). I had still the drives attached when I made this shot.

Having fun with the polar block

The polar block can be a real trouble maker when disassembled the first time. I had to excert brute force to open the four screws seen in Figs. 8 & 9.

Fig. 7: That's where you start from. Remove the two screws in the middle of the base plate that lock the azimuth. You don't need to remove the two big cylindrical screws in front.

Fig. 8: Turn the polar block upside down, and remove the big screw (image: lower middle) that holds the round black plate (lower left) in place. After this step you can pull the upper part of the polar block (upper left) from its base plate (upper right). Locate the four big allen head screws in the upper part of the polar block and remove them.

Fig. 9: After removing the four screws the piece with the big polar height adjustment knob comes off. Unscrew the two allen head screws on its front, then take away the little black plate that was held in place by them. The situation will now look like this.

Fig. 10: View from below on the polar height adjustment mechanism. Turning the big knob moves the golden cylinder along the screw, thus adjusting the inclination of the RA block. You'll probably find quite some golden powder that was abrased from the bolt during earlier operation.

Fig. 11: You can see a small allen head locking screw in the big polar adjustment knob. Losen it. Hold the left end of the long screw in Fig. 10 with a gripper and unscrew the big knob. Further disassembly is self explanatory. The black cylinder that can be found on the long screw can be losened and shifted. In this way you can control the strength and the backlash of the polar height adjustment process. You might want to leave this piece in its place.

Disassembling the RA and the DEC blocks

The RA and the DEC block are very similar. Quite some parts such as worms and worm gears or roller bearings can be exchanged, which is very useful for trouble shooting. I describe the disassembling for the RA block only, since it is identical for the DEC block. You start with the big black respectively silver clutch knobs that are used for tightening the RA and the DEC axes (see Fig. 6). A number of washers and needle bearings come off, remember their order. Depending on whether you use the Losmandy Digital Setting Circles (DSC) or not, the number of washers will be even greater.

Fig. 12: Once the clutch knob and the washers came off, you can simply pull out the axis to the other side. The order of things from the outside to the inside is: clutch knob, curved washer, thin washer, roller bearing, thick washer, gear for the DSC, thick washer, roller bearing, thin washer.

Fig. 13: The RA block with the axis removed. The setting circle is attached to the big gear by the three screws. You can remove it if you like, or directly pull the big gear with the setting circle attached to it (see Fig. 16 directly below).

Fig. 14: Close-up of the upper needle bearing. Possibly, this bearing needs thorough cleaning and some fresh grease. In particular older mounts will appreciate that a lot.

Fig. 15: The lower needle bearing. The big cone-shaped lower part can be rotated in its bearings. A strong hit on the side of the motor can cause such a rotation. Take a hammer and gently knock on the side of the flat plate in Fig. 16 to rotate it back into position. The mount doesn't seem to take damage during this operation.

Fig. 16: The big gear can be simply pulled off.

Fig. 17: Beneath the gear you will find two thin washers, then a roller bearing, and at the bottom a thick washer. Inside sits a very thick aluminum ring. You should oil the roller bearing, and slightly grease the interfaces between the other washers.

Fig. 18: The big washers from beneath the gear are removed. Very old G11s don't have the smaller aluminum ring, and the four big washers are much smaller. I guess that is why the very old mounts have a reduced payload of 15 kgs as compared to 25 kgs.

Fig. 19: For completeness; shown is the partially disassembled DEC block. Note the hole in the DEC axis for the polar finder, and the big whiteish nylon washer on top of the axis. This is the coupling. Both of its surfaces must be free of any grease, otherwise the coupling doesn't work properly. The same holds for the white coupling seen in Fig. 12 on the RA axis.